A method for cleaning compressed air in a compressed air supply system of a motor vehicle is known from the PCT Application published under WO 01/26783 A1 and corresponding to U.S. Pat. No. 6,723,154 B2. The compressed air coming from a compressor and especially including oil and water is cleaned by first passing it through a pre-filter, then through a layer of silica gel, then through a molecular sieve and finally through a fine filter. The pre-filter serves to collect larger solid particles, water particles as well as liquids and other substances and to prevent them from further passage. The pre-filter has a good efficiency with respect to larger particles, for example particles larger than 5 μm, but at the same time a rather bad efficiency with respect to smaller particles. Silica gel having large pores and silica gel having fine pores are arranged one after the other in a second chamber of a deposit zone. The silica gel with large pores serves to collect larger carbon compounds and other chemical compounds. It also serves to take up water in liquid form. The silica gel having fine pores serves to take up smaller carbon compounds and water in vapor form. These two kinds of silica gel are arranged in one common deposit chamber. The direction of flow of the compressed air to be cleaned is directed against gravity. Next, there is another deposit chamber in which a molecular sieve is arranged. Finally, the compressed air passes beyond a fine filter which is suitable to take up and to deposit smaller particles. The majority of deposit chambers including the separate treatment substances are located one after the other in a deposit zone in a cartridge. The cartridge is designed to be replaceably connected to a base element. Despite the arrangement of the plurality of separate treatment layers, the deposit effect for oil mist is not optimal. Such oil mist has a negative effect on the reliable functionality of valves being located in the system.
A replaceable cartridge for cleaning compressed air in compressed air supply systems of motor vehicles is known from the PCT Application published under WO 01/52973 A1. The known cartridge includes a housing in which a deposit chamber is arranged, the deposit chamber being filled with a treating substance. The treating substance substantially serves to take up humidity from the air to be cleaned. A coalescence filter is arranged at the entrance side of the deposit chamber being filled with a treating substance. The coalescence filter may include laminated fibers or a fiber mat, and it serves to take up oil vapors from the introduced air flow to protect the treating substance being located downstream from contacting such oil vapor. The coalescence filter is designed and arranged in a conical way such that the deposited oil is collected at the radial outer circumference of the coalescence filter. During regeneration of the cartridge, the coalescence filter is lifted from its seat in an upward direction such that the collected oil is removed by the regeneration air flow.
A replaceable cartridge for cleaning compressed air in compressed air supply systems of motor vehicles is known from US Patent Application No. US 2004/0016342 A1. The known cartridge includes a deposit chamber being located inside of a housing and being filled with a treating substance. The deposit chamber serves to take up humidity from the compressed air to be cleaned. A coalescence filter is arranged at the entrance side of the deposit chamber. The coalescence filter consists of fiberglass and the like and it serves to deposit oil or oil mist to keep it away from the following treating substance. At the exit side, the coalescence filter is surrounded by a sucking material which serves to transport deposited drops of oil into a collecting chamber. The coalescence filter is bypassed by a bypass conduit in which a check valve is arranged, the check valve opening during regeneration of the cartridge. The compressed air to be cleaned coming from the compressor is first introduced into the coalescence filter which causes the danger of clogging effects occurring at the coalescence filter and the coalescence filter loosing its efficiency.
An air dryer is known from the PCT Application published under WO 94/26569 corresponding to U.S. Pat. No. 5,286,283. An oil filter is located upstream of the deposit zone including the treating substance for taking up humidity. The oil filter serves to deposit oil. The collected oil is transported into the deposit chamber, and it cannot be removed before regeneration, the oil being removed through a bypass conduit connecting the deposit chamber to the entrance and bypassing the oil filter during regeneration.
An air filter is known from U.S. Pat. No. 5,002,593. The air filter includes a deposit chamber being filled with a drying agent. An oil separator and an oil filter are located upstream of the entrance of the deposit chamber.
All these known constructions of air filters and cartridges, respectively, have in common that the coalescence filter is arranged at the entrance of the air dryer and that the coalescence filter serves to remove oil from the compressed air to be cleaned coming from the compressor such that there is no negative influence on the deposit chamber for humidity being filled with a drying agent and being located downstream. Direct introduction of the flow of compressed air coming from the compressor into the coalescence filter causes comparatively great load acting upon the coalescence filter. There is the danger of the coalescence filter clogging due to drops of water, drops of oil, coke particles and similar larger cluster-like elements such that the positive effect of the coalescence filter quickly decreases. In this way, the desired protection of the deposit chamber including the drying agent and being located downstream is no longer ensured.
Another air dryer and a method for removing water from air are known from the PCT Application published under WO 99/21641.
Another air dryer is known from German Patent Application No. DE 103 29 401 A1. This document includes a FIG. 3 which is prior art with respect to the invention disclosed in this document. FIG. 3 shows an air dryer in which a filter being designated as a fleece filter is located upstream of a drying insert being filled with a drying agent. This document considers the prior art air dryer according to FIG. 3 as causing problems in the sense of the fleece filter being polluted over time which results in a reduction of the filter effect and which makes it necessary to replace the filter. To overcome these drawbacks, this document teaches an air dryer as illustrated in FIG. 1. This air dryer does not include a fleece filter, but instead only a coalescence filter being arranged at the entrance side upstream of a drying insert. In this way, the compressed air including solid impurities and liquid impurities is introduced into the coalescence filter via a chamber which is located upstream of the coalescence filter. This chamber does not include any filter material. Only in the embodiment of FIG. 2 of this document, a small part of this chamber includes a fleece filter which covers the coalescence filter at one side and which only has a small thickness through which the flow is guided. A check valve is located below this packet being formed by the fleece filter and the coalescence filter. A check valve is designed and arranged such that the polluted compressed air is initially forced through the fleece filter and then through the coalescence filter. During regeneration, the compressed air bypasses the fleece filter such that impurities contained in the fleece filter are not removed from the fleece filter. Consequently, there is no forced flow though the fleece filter and thus no forced cleaning of the fleece filter during the regeneration phase.